The present invention relates to a high-frequency power amplifier module for amplifying high-frequency signal and particularly to a high-frequency power amplifier module that may be used suitably to a dual-band system radio equipment that can transmit and receive a couple of band frequencies.
In the European digital cellular system that is now put into the service as the mobile communication system, it is assumed in the GSM (Global System for Mobile Communication) using the frequency of 0.9 GHz band that subscribers will exceed the system capacity in near future. Therefore, the mobile telephone apparatus (hand-held telephone) corresponding to the dual-band system using, in combination with the GSM system, the DCS (Digital Cellular System) 1800 system using the frequency band near 1.8 GHz is requested because this system is similar to the GSM communication system in such a point that the same modulation system GMSK (Gaussian-filtered Minimum Shift Keying) is introduced.
Here, since above two systems (GSM system and DCS1800 system) are almost used in common except for the frequency, it is possible to structure the hand-held telephone set that is used in common in the GSM/DCS1800 systems by providing only the high frequency unit such as the power amplifier module that can be used for dual band system.
Therefore, in order to achieve the power amplifier module corresponding to the dual-band system, two power amplifier module systems corresponding to each communication system are integrated within the module and are structured to selectively switch each system as required.
FIG. 7 illustrates a schematic structure of the mobile telephone apparatus discussed prior to the present invention. In the same figure, a reference numeral 13 designates a blanching filter; 14, a dual-band transmitting/receiving antenna; 15, a first radio frequency power amplifier module (RF power module) ; 16, a second RF power module; 17, a wide-band amplifier (WAMP); 18, a radio frequency signal processing unit (RFSPU) ; 19, a system control unit (CNTU) consisting of the central processing unit (CPU) ; 20, an operation panel (OP) ; 21, a transceiver consisting of a speaker (SP) and a microphone (MIC) or the like. Vcc designates the power supply voltage. Moreover, the communication systems that can be used through the switching operation include the GSM system and DCS1800 system.
A radio signal processing circuit 18 is comprised of a modem processing unit, transmitting/receiving IF (intermediate frequency) unit and frequency converting unit (up-/down-converter) or the like and a radio signal (f1 or f2) of any one of the GSM system of 0.9 GHz band or the DCS1800 system of 1.8 GHz band selected is generated and output at the transmitting time. These two kinds of radio transmitting signals f1, f2 are input respectively to the first RF power module 15 and the second RF power module 16.
The RF power module 15 is a power amplifier module corresponding to the GSM communication system and is comprised of an RF power MOS field effect transistor T1 for final stage amplifier, matching circuits MC1 and MC2 consisting of passive elements, and an inductance element Lc1 for DC choke of drain bias. In this case, the transistor T1 is formed to provide an output, through the switching of a gate voltage to cutoff bias level and predetermined bias level, with the first bias control signal 22 output from the CPU of system control unit 19 interlocked with the GSM/DCS1800 selection switch of the mobile communication apparatus body.
In the same manner, the RF power module 16 is the power amplifier module corresponding to the DCS1800 communication system and is comprised of the RF power MOS field effect transistor T2 for final stage amplifier, matching circuits MC3 and MC4 consisting of passive elements, and inductance element Lc2 for DC choke of drain bias. In this case, the transistor T2 is formed to provide an output, through the switching of gate voltage impressed to the transistor T2 to the cutoff bias level and the predetermined bias level with the second bias control signal 23 output from the CPU of system control unit 19 interlocked with the GSM/DCS1800 selection switch of the mobile communication apparatus body.
The RF power modules 15 and 16 are respectively designed in optimum to set the matching with the matching circuits MC1 to MC4 so that the radio signals of the respective communication systems can be amplified effectively.
Thereby, the apparatus is operated as a hand-held telephone set of the GSM system, the bias control signal 22 of the RF power module 15 is set to the predetermined bias level and meanwhile the bias control signal 23 of the RF power module 16 is set to the cutoff bias level. Thereby, it is possible to selectively operate only the RF power module 15 to amplify the GSM radio signal f1 (0.9 GHz band).
When the apparatus is operated as a hand-held telephone set of the DCS1800 system, the bias control signal 23 of the RF power module 16 is set to the predetermined bias level and meanwhile the bias control signal 22 of the RF power module 15 is set to the cutoff bias level, thereby only the RF power module 16 is selectively operated to amplify the DCS1800 radio signal f2 (1.8 GHz band).
The structure explained above is selectively used depending on the setting of communication system by respectively providing the exclusive RF power modules within the apparatus for two communication systems. The RF power modules provided within the apparatus are designed in the optimum manner for respective communication system, assuring economical and effective operation.
Moreover, the radio frequency power amplifier module used in the hand-held telephone set is required to satisfy the specifications of the high frequency characteristic determined by each system such as the output power and is also required to satisfy further high efficiency and reduction in size.
Here, the technique to control the harmonics is well known as the technique to realize further high efficiency operation of the power amplifier for transmitter. For example, the Japanese Published Unexamined Patent Application No. SHO 60(1985)-109310 discloses the structure that one end part of the 1/4 wavelength transmission line is terminated at a higher frequency, while the other end thereof is connected to an amplifier element and a series resonant circuit to obtain the desired basic waveform signal output from the serial resonant circuit. With this structure, the connecting point of the output side of the amplifying element and 1/4 wavelength transmission line is terminated for the basic waveform and odd number order harmonics and thereby the ideal class F operation mode in which a current and a voltage at the output terminal of the amplifying element become zero can be obtained, and high efficiency can also be attained.
The high frequency power amplifier circuit of the related art forms a power amplifier circuit, as illustrated in FIG. 8(a), by connecting the other end of the 1/4 wavelength transmission line 24 with one end thereof is terminated for high frequency signal to the output side of an amplifying element 25 and one end of a series resonance circuit 26 and the other end of the series resonance circuit 26 to an output terminal 27. Here, when the amplifying element 25 operates upon input of a basic signal, the voltages are distributed on the 1/4 wavelength transmission line 23. FIG. 8(b) illustrates the condition of voltage distribution on the 1/4 wavelength transmission line 24. This voltage distribution can be obtained for signal inputs of basic frequency signal and double-frequency signal. Sine one end II of the 1/4 wavelength transmission line 24 is perfectly terminated for high frequency signal, the voltages are applied to the connection part I to open for the basic frequency signal and to terminate for the double-frequency signal. Moreover, above voltage distribution is similar to the third harmonics or higher and the connection part I is opened for all odd number order harmonics as in the case of the basic frequency signal and is terminated as in the case of the double-frequency signal for all even number order harmonics.
However, when the high efficiency technique is applied to the circuit structure of FIG. 7 explained above, a couple of power amplifier modules adding the circuit for harmonics control as explained above are required, resulting in the disadvantage that the circuit configuration becomes large in size.
Accordingly, it has been expected that the structure of the radio frequency power amplifier module is designed to realize the radio frequency power amplifier module corresponding to high efficiency dual-band system to be used in a couple of frequency bands for one system using in common the one-input and one-output driving stage amplifier and radio frequency output transistor for two communication systems.
Moreover, a method for controlling the harmonics using the 1/4 wavelength transmission line of the related art has a problem when the power amplifier module is adopted to the hand-held telephone system for two different frequencies as in the case of the structure illustrated in FIG. 7. For example, when the related art is applied to the hand-held terminals that is used in common to the GSM system using the frequency around 0.9 GHz band and the DCS1800 system using the frequency around 1.8 GHz band, the transmission lines are respectively required for the GSM and DCS1800 systems and therefore it is difficult to reduce the size of the apparatus. Moreover, since requirement for reduction in size of package is quite intensive in recent years, it is very difficult to comprise the (1/4)-wavelength transmission lines for 0.9 GHz and 1.8 GHz within the same package.
In addition, in the case of the method wherein the circuit configuration is comprised of the power amplifier only for GSM system and the power amplifier only for DCS1800 system and both circuits are selectively used, reduction in size is quite difficult because a couple of power amplifiers are provided.
For reduction in size, it is effective that the drive stage amplifier used in the radio frequency power amplifier modules for GSM system and DCS1800 system, and the radio frequency power output transistor are used in common for both systems. However, here rises a problem that efficiency is lowered because output power is different to a large extent in both systems.
The present invention has been proposed to solve such problem and it is therefore an object of the present invention to provide a small size and high efficiency power amplifier module corresponding to the dual-band communication system using in common two kinds of frequencies.
The radio frequency power amplifier module of the present invention can be suitably used for the dual-band type radio apparatus that can transmit or receive two kinds of band frequencies f1, f2 (f1 less than f2), the drive stage amplifier and radio frequency power transistor forming this radio frequency power amplifier module can be used in common for the radio signal of both systems, and an output stage circuit including the radio frequency power output transistor is formed of a radio frequency power output transistor, a transmission line connected to the drain end of the radio frequency power output transistor to control the radio frequency power, a parallel resonance circuit connected in series with this transmission line, a series resonance circuit connected in series and an output matching circuit matched with the band frequencies of both systems to extract the basic frequency element.
Here, the parallel resonator is set to resonate at the frequency corresponding to the predetermined even number order harmonics of the band frequency f2, while the transmission line is set to terminate for the even number order harmonics in the impedance of the drain end using a parasitic reactance existing at the drain of the radio frequency power output transistor. Moreover, the constants of the circuit elements forming the parallel resonator are set so that the impedance of drain end is opened for the predetermined odd number order harmonics of the frequency f1 through combination of the series resonator that is set to resonate at the frequency corresponding to the predetermined odd number order harmonics of the band frequency f1, transmission line and parasitic reactance of the radio frequency power output transistor.
With such structure, when the power amplifier module is operated, the harmonics signal is controlled for the radio signal of the system. Therefore, generation of heat that is generated when a product of the current and voltage at the output terminal of the radio frequency power output transistor of the power amplifier module does not become zero can be controlled and thereby efficiency can be improved. Namely, it is now possible to form the high efficiency and small size radio frequency power amplifier module corresponding to the dual-band system.